Once? No jellyfin has had about 4 major RCE issues since the fork. At least 4 that I'm aware of. Blaming it on the previous code only makes sense if the split is recent. They have had time to completely rewrite if they really want.
I'd like to see plex die entirely, but I know too many less technical people that use it . They are not going to set up a VPN , end of story end of discussion. And I'm not going to tell them to use jellyfin when it will likely continue to have major security issues and could compromise their systems. I have no doubt that Plex leadership is fully aware of this, they know that even with them pushing more subscriptions and higher costs they are going to continue to have users because the alternatives are just not able to keep up and are not viable for the average person just the technical users which they would have lost to alternatives regardless